I've use this for me. It works.
https://www.busche.org/index.php/2021/03/21/ipv4-ueber-wireguard-von-opnsense-zu-opnsense-routen-cgnat-umgehen/
https://www.busche.org/index.php/2021/03/21/ipv4-ueber-wireguard-von-opnsense-zu-opnsense-routen-cgnat-umgehen/